Self-limiting fin spike removal

ABSTRACT

Provided is a method for forming a semiconductor structure. In embodiments of the invention, the method includes laterally forming a spacer on a side of the semiconductor structure. The method further includes performing a thermal anneal on the semiconductor structure. The method further includes performing an etch to remove materials formed by the thermal anneal.

BACKGROUND

The present invention relates in general to field effect transistors(FETs). More specifically, the present invention relates to FETs withimproved fin construction.

Integrated circuit devices are a set of electronic circuits on one smallchip of semiconductor material. A typical integrated circuit deviceincludes many transistors. As feature sizes have become smaller,different types of transistor architectures have been developed. Amongthe newer types of transistor architectures is the fin-type field effecttransistor (FinFET).

SUMMARY

One or more embodiments of the invention provide a method for forming asemiconductor structure. In embodiments of the invention, the methodincludes laterally forming a spacer on a side of the semiconductorstructure. The method further includes performing a thermal anneal onthe semiconductor structure. The method further includes performing anetch to remove materials formed by the thermal anneal.

One or more embodiments of the invention provide a semiconductorstructure. The semiconductor structure includes a substrate. Thesemiconductor structure further includes one or more fin regionscontacting the substrate and extending in a first direction. Thestructure further includes a shallow trench isolation region contactingthe substrate and between the one or more fin regions. The fin region isformed by laterally forming a spacer on a side of the semiconductorstructure. The method further includes performing a thermal anneal onthe semiconductor structure. The method further includes performing anetch to remove materials formed by the thermal anneal.

One or more embodiments of the invention provide a semiconductorstructure. The semiconductor structure includes a substrate. Thesemiconductor structure further includes one or more fin regions eachoverlaying a strain relief buffer region contacting the substrate andextending in a first direction. The structure further includes a shallowtrench isolation region contacting the substrate and between the one ormore fin regions. The fin region is formed by laterally forming a spaceron a side of the semiconductor structure, in a direction perpendicularto a substrate of the semiconductor. The method further includesperforming a thermal anneal on the semiconductor structure. The methodfurther includes performing an etch to remove materials formed by thethermal anneal.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of embodiments is particularly pointed out anddistinctly defined in the claims at the conclusion of the specification.The foregoing and other features and advantages are apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 depicts a cross-sectional view of a standard fin-type fieldeffect transistor;

FIG. 2A depicts a cross-sectional view of a semiconductor with a partialfin;

FIG. 2B depicts a cross-sectional view of a semiconductor after aprocessing operation;

FIG. 2C depicts a cross-sectional view of a semiconductor after aprocessing operation;

FIG. 3 depicts a cross-sectional view of the semiconductor structure;

FIG. 4A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 4B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 5A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 5B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 6A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 6B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 7A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 7B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 8A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 8B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 9A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 9B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 10A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 10B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 11 depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 12A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 12B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 13A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 13B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 14A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 14B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 15A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 15B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 16A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 16B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 17A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 17B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 18A depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 18B depicts a cross-sectional view of the semiconductor structureafter a processing operation according to one or more embodiments of thepresent invention;

FIG. 19A depicts a chemical equation according to one or moreembodiments of the present invention; and

FIG. 19B depicts a cross-sectional view of an exemplary chemicalreaction according to one or more embodiments of the present invention.

DETAILED DESCRIPTION

Typical semiconductor devices are formed using active regions of awafer. The active regions are defined by isolation regions used toseparate and electrically isolate adjacent semiconductor devices. Forexample, in an integrated circuit having a plurality of metal oxidesemiconductor field effect transistors (MOSFETs), each MOSFET has asource and a drain that are formed in an active region of asemiconductor layer by implanting n-type or p-type impurities in thelayer of semiconductor material. Disposed between the source and thedrain is a channel (or body) region. Disposed above the body region is agate electrode. The gate electrode and the body are spaced apart by agate dielectric layer.

One particularly advantageous type of MOSFET is known generally as afin-type field effect transistor (FinFET). A three-dimensional view ofan exemplary FinFET 100 is shown in FIG. 1. The basic electrical layoutand mode of operation of FinFET 100 do not differ significantly from atraditional field effect transistor. FinFET 100 includes a semiconductorsubstrate 102, a shallow trench isolation (STI) layer 104, a fin 106 anda gate 114, configured and arranged as shown. Fin 106 includes a sourceregion 108, a drain region 110 and a channel region 112, wherein gate114 extends over the top and sides of channel region 112. For ease ofillustration, a single fin is shown in FIG. 1. In practice, FinFETdevices are fabricated having multiple fins formed on STI 104 andsubstrate 102. Substrate 102 can be silicon, and STI 104 can be an oxide(e.g., SiO₂). Fin 106 can be silicon that has been enriched to a desiredconcentration level of germanium. Gate 114 controls the source to draincurrent flow (labeled ELECTRICITY FLOW in FIG. 1). In contrast to aplanar MOSFET, however, source 108, drain 110 and channel 112 are builtas a three-dimensional bar on top of STI layer 104 and semiconductorsubstrate 102. The three-dimensional bar is the aforementioned “fin106,” which serves as the body of the device. The gate electrode is thenwrapped over the top and sides of the fin, and the portion of the finthat is under the gate electrode functions as the channel. The sourceand drain regions are the portions of the fin on either side of thechannel that are not under the gate electrode. The dimensions of the finestablish the effective channel length for the transistor.

The semiconductor substrate 102 can be, for example, a bulksemiconductor material such as silicon, or a semiconductor-on-insulator(SOI) substrate including a handle substrate, a buried insulator layer,and a top semiconductor layer. In some embodiments of the invention, thesubstrate can include a semiconductor material, such as, for example,Si, Ge, SiGe, SiC, SiGeC, and III/V compound semiconductors. Thesubstrate can provide mechanical support to the fin, STI, and otherlayers. The thickness of the substrate can be, for example, from 30 μmto about 2 mm.

Turning now to a more detailed description of technologies that are morespecifically relevant to aspects of embodiments of the presentinvention, an issue that can occur during semiconductor fabrication isthat lithography overlay can result in portions of a fin remaining afterfin cut patterning. If you performed an isotropic etch to remove theportion of the fin, an intact fin could be weakened. Current FinFETtechnology requires removal of fins from the region where no fins aredesired so that fins are formed only in the regions where they needed. Afin cut mask is applied to remove the undesired fins. However, due tothe inherent variation of lithography process, the fin removal processwill become extremely challenging to precisely place the mask relativeto the fin patterns, especially for closely packed fins. An excessivemisalignment of the fin cut mask to the fins will result in either anincomplete removal of unwanted fins, or a partial removal of the actualdevice fins. Both can result in a yield issue.

FIGS. 2A through 2C illustrate the above-described issue. In FIG. 2A, aportion of a semiconductor wafer is shown in a cross-sectional view.Atop substrate 205 are fins 210 and 212 and shallow trench isolation(STI) layer 215. Atop fins 210 and 212 are hard masks 220 and 222,respectively. At the right side of the semiconductor wafer is a partialfin 218 and partial hard mask 228. FIG. 2B illustrates the same waferafter a processing step has been performed. An etch is performed toremove partial fin 218 and partial hard mask 228. The result is shown inFIG. 2C—the etch has damaged a portion of fin 212 (portion 227). Becauseof the defect seen in FIG. 2C, portions of the semiconductor wafer (oreven the entire semiconductor wafer) could be rendered unusable.

Turning now to an overview of one or more embodiments of the invention,the use of a thermal anneal process on a spacer material in anoxygen-free environment is presented. In one or more embodiments of theinvention, the resulting structure can feature no partial fins, with noweakening of the remaining fins. Methods for forming a semiconductorstructure and semiconductor structures in accordance with embodiments ofthe invention are described in detail below by referring to theaccompanying drawings in FIGS. 3-19B.

FIG. 3 depicts a cross-sectional view of a semiconductor structure aftera processing operation according to one or more embodiments of theinvention. As depicted in FIG. 3, the semiconductor structure caninclude a substrate 305. Substrate 305 can be silicon. Fins 310 and 312are formed on substrate 305. Fins 310 and 312 can be formed of a silicongermanium (SiGe) material. A hard mask 320 and 322 are placed on fins310 and 312, respectively. Thereafter, an STI layer 315 is deposited tocover the fins 310 and 312 and hard mask 320 and 322. Thereafter achemical mechanical polish (CMP) is performed to remove the extra STImaterial and stop on top of the fin hard mask.

The hard mask layer 320 (and 322) can include an oxide, nitride,oxynitride or any combination thereof including multilayers. In someembodiments of the invention, the hard mask layer 320 (and 322) caninclude silicon oxide or silicon nitride. The hard mask layer 320 (and322) can be formed utilizing a deposition process such as, for example,chemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), chemical solution deposition, evaporation. In someembodiments of the invention, the hard mask layer 320 (and 322) can beformed by a thermal process such as, for example, oxidation ornitridation of the top semiconductor layer. Any combination of the abovementioned processes can also be used in forming the hard mask layer 320(and 322). The hard mask layer 320 (and 322) can have a thickness from20 nm to 80 nm, for example, from 30 nm to 60 nm.

At the right side of the figure is a fin 318 and corresponding hard masklayer 328. In some embodiments, fin 318 can be partially cut off. Insome embodiments, fin 318 otherwise can be judged unusable. Therefore,fin 318 and hard mask 328 can be subject to removal.

FIGS. 4A and 4B depict a cross-sectional view of a semiconductorstructure after a processing operation according to one or moreembodiments of the invention. In FIGS. 4A and 4B, two separate cases areshown. The cases are similar to those shown in FIG. 3, with the additionof a mask. In FIG. 4A, mask 430 is deposited over fins 310 and 312, withfin 318 uncovered by mask 430. In FIG. 4B, mask 432 is deposited overfins 310 and 312 and partially deposited over fin 319. Due to the smalldistance between the fins 310, 312, and 319, it is not always possibleto exactly place deposit mask 430 or 432. So two different possibilitiesare illustrated in FIGS. 4A and 4B. This condition also can be referredto as an overlay condition, because mask 432 is partially overlaying fin319.

Mask 430 and 432 can be constructed of one of a variety of differentmaterials. In some embodiments, mask 430 and 432 can be a soft mask(such as a photoresist) or a hard mask (such as a silicon oxide or asilicon nitride).

FIGS. 5A and 5B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. The structure resulting from a reactiveion etch (RIE) is illustrated in FIGS. 5A and 5B. The RIE is configuredto remove any structure above the substrate 305 that is not covered bymask 430 or mask 432. In FIG. 5A, the entire fin 318 is removed (whichwas present in FIG. 4A). In FIG. 5B, only a portion of fin 319 remains.

FIGS. 6A and 6B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. A germanium oxide (GeO₂) spacer islaterally formed along the side of the structure. The formation canoccur in one of a variety of different manners known in the art, such asconformal thin film deposition (e.g., using ALD), possibly followed by adirectional RIE. In FIG. 6A, GeO₂ spacer 630 is in contact with STIlayer 315. In FIG. 6B, GeO₂ spacer 633 is illustrated as contacting aportion of dummy fin 319. The thickness of GeO₂ spacer 630 and 633 has aself-limiting modification on the SiGe in the lateral direction.

FIGS. 7A and 7B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. A thermal anneal is performed in a nooxygen environment (e.g., in a nitrogen environment or in an inert gasenvironment). The silicon in the SiGe channel reacts with the germaniumoxide to form silicon oxide (SiO₂).

In FIG. 7A, the GeO₂ spacer (630 and 633) reacts to the thermal anneal,resulting in an area of silicon oxide (SiO₂) 740 at the bottom, above anarea of silicon germanium (SiGe) with a high percentage of germanium(742). The remainder of the GeO₂ remains as reference 630. In contrast,in FIG. 7B, the SiGe of fin 317 reacts to turn the SiGe into siliconoxide 745. The remainder (747) is silicon germanium with a highpercentage of germanium.

The chemistry behind this reaction is shown in FIG. 19A-19B. Silicon inan area of SiGe is selectively oxidized due to the lower Gibbs freeenergy. The chemical equation is shown in FIG. 19A, as silicon andgermanium added to germanium oxide (when in a thermal anneal performedin an oxygen-free environment) results in germanium, volatile speciesgermanium oxide, and silicon oxide. In embodiments of the invention, theabove-described reaction process can be well-controlled, as the reactionof GeO₂ with the SiGe only occurs during the anneal, which can, in someembodiments be a spike anneal at a temperature of from about 450 toabout 700 degrees Celsius, depending on the Ge concentration in theSiGe. At these temperatures, there is no reaction of the GeO₂ with puresilicon, STI or hardmask material. Accordingly, the annealing method ofthe present invention is highly selective to SiGe. During the thermalanneal process, the reaction of GeO₂ with SiGe selectively oxidizessilicon in the exposed SiGe region and condenses germanium in theremaining SiGe according to the reaction described in FIG. 19A. As thereaction proceeds, more Si in the SiGe region is oxidized to SiO₂, andthe surface of the SiGe portion is continuously enriched with moregermanium.

FIG. 19B illustrates an exemplary process performed on a structure 1950.Structure 1950 includes a layer 1952 of silicon, a layer 1954 of silicongermanium (with a 20 percent concentration of germanium), and a layer1956 of germanium oxide. As shown in the illustration, layer 1952 isapproximately 20 nm thick while layer 1954 is approximately 3 nm thick.

Structure 1950 is subjected to a thermal anneal at a temperature betweenabout 450 to about 700 degrees Celsius, depending on the Geconcentration in the SiGe, in a nitrogen atmosphere. While a nitrogenatmosphere is shown for illustrative purposes, it should be understoodthat hydrogen can be used in some embodiments. In other embodiments, aninert gas, such as argon, or mixture of gases also can be used.

After the thermal anneal is performed, the result is structure 1960.Structure 1960 includes a layer 1962 of silicon. Atop layer 1962 is alayer 1964 of silicon germanium (with a 20 percent concentration ofgermanium), followed by a layer 1966 silicon germanium (with a 40percent concentration of germanium), followed by a layer 1968 of siliconoxide. The thickness of layer 1964 is approximately 16 nm, the thicknessof layer 1966 is approximately 3 nm, and the thickness of layer 1968 isapproximately 3 nm. The non-reacted GeO₂ is water soluble, so can easilybe removed with a water solution, such as de-ionized water.

FIGS. 8A and 8B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. An isotropic etch is performed of thesilicon oxide (740 and 745 of FIGS. 7A and 7B) formed by the GeO₂reaction. The isotropic etch could be, for example, a hydrofluoric acidwet etch or dry etch. The remaining GeO₂ is stripped by water, leavingjust areas 742 and 747 containing silicon germanium with a highpercentage of germanium, compared to that of original SiGe.

FIGS. 9A and 9B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. Areas 742 and 747 of FIGS. 8A and 8B areremoved. This can be performed in one of a variety of different manners.For example, an isotropic etch such as gas phase etch, plasma etch, orwet etch. For example, in the case where SiGe fins comprise Si₈₀Ge₂₀,the isotropic etch selectively removes the as formed high Ge % (i.e.,Si₆₀Ge₄₀) sacrificial layers relative to the low Ge % (i.e., Si₈₀Ge₂₀)fin layer. In one embodiment, the high Ge % SiGe etch process includesgas phase hydrogen fluoride etch, a wet etch process containing a mix ofammonia and hydrogen peroxide, a dry etch such as plasma etch.

FIGS. 10A and 10B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. Above substrate 205, an etch is performedto remove the hard mask (220 and 222). A fill is performed to add toshallow trench isolation (STI) layer 215 to the areas removed in earliersteps. In addition, a recess can be performed to partially removeportions of STI layer 215, exposing fins 210 and 212. From this point,traditional semiconductor processing steps can be performed to finishthe semiconductor device fabrication.

FIG. 11 depicts an alternative embodiment of the above describedprocess. As opposed to the uniform silicon germanium fin depicted inFIGS. 3 through 10B, the fin in FIGS. 11 through 18B include a silicongermanium (SiGe) strain relaxed buffer (SRB) layer that is above asilicon substrate. Thereafter, a silicon fin is grown over the SRBlayer.

As depicted in FIG. 11, the semiconductor structure can include asubstrate 1105. Silicon fins 1110, 1112, and 1118 are each formed on anSRB layer 1107. Thereafter, an STI layer 1115 is used to fill the regionbetween fins 1110, 1112, 1118, and the respective SRB layers 1107. Hardmask layers 1120, 1122, and 1128 are atop fins 1110, 1112, and 1118,respectively. Thereafter a chemical mechanical polish (CMP) isperformed.

FIGS. 12A and 12B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. In FIGS. 12A and 12B, two separate casesare shown. The cases are similar to those shown in FIG. 11, with theaddition of a mask. In FIG. 12A, mask 1230 is deposited over fins 1110and 1112, with fin 1118 uncovered by mask 1230. In FIG. 12B, mask 1232is deposited over fins 1110 and 1112 and partially deposited over fin1119.

FIGS. 13A and 13B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. The structure resulting from a reactiveion etch (RIE) is illustrated in FIGS. 13A and 13B. The RIE isconfigured to remove any structure above the substrate 1105 that is notcovered by mask 1230 or mask 1232. In FIG. 13A, the entire fin 1118 isremoved. In FIG. 13B, a portion of fin 1119 remains.

FIGS. 14A and 14B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. A germanium oxide (GeO₂) spacer islaterally formed along the side of the structure. The formation canoccur in one of a variety of different manners known in the art, such asconformal thin film deposition (e.g., using ALD), possibly followed by adirectional RIE to remove the germanium oxide layer on horizontalsurfaces. In FIG. 14A, GeO₂ spacer 1430 is in RIE 1115, shown close tofin 1112. In FIG. 14B, GeO₂ spacer 1433 is illustrated as contacting aportion of dummy fin 1119. The =GeO₂ spacer 1430 and 1433 has aself-limiting modification on the SiGe in the lateral direction as wellas on the top surface portion of the adjacent SiGe in the verticaldirection.

FIGS. 15A and 15B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. A thermal anneal is performed in a nooxygen environment (e.g., in a nitrogen environment or in an inert gasenvironment). The silicon in the SiGe is selectively oxidized, due tothe lower Gibbs free energy, to form silicon oxide (SiO₂).

In FIG. 15A, the GeO₂ spacer (1430 and 1433) reacts to the thermalanneal, resulting in an area of silicon oxide (SiO₂) 1542 at the bottom,above an area of silicon germanium (SiGe) with a high percentage ofgermanium (1540). The remainder of the GeO₂ remains as reference 1430.In contrast, in FIG. 15B, the SiGe portion of fin 1119 reacts to turnthe SiGe into silicon oxide 1545. There is no reaction between Siportion of the fin and the GeO₂ spacer and remains as reference 1433.The remainder (1547) is silicon germanium with a high percentage ofgermanium.

FIGS. 16A and 16B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. An isotropic etch is performed of theoxide (1540 and 1545 of FIGS. 15A and 15B) formed by the GeO₂ reaction.The remaining GeO₂ is stripped by water, leaving just areas 1542 and1547 containing silicon germanium with a high percentage of germanium.

FIGS. 17A and 17B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. Areas 1542 and 1547 of FIGS. 15A and 15Bare removed. This can be performed in one of a variety of differentmanners aforementioned.

FIGS. 18A and 18B depict a cross-sectional view of the semiconductorstructure after a processing operation according to one or moreembodiments of the invention. Above substrate 1105, an etch is performedto remove the hard mask (1120 and 1122). A fill is performed to add toshallow trench isolation (STI) layer 1115 to the areas removed inearlier steps. In addition, a recess can be performed to partiallyremove portions of STI layer 1115, exposing fins 1110 and 1112. Fromthis point, traditional semiconductor processing steps can be performedto finish the semiconductor.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of embodiments of the presentinvention. It is noted that various connections and positionalrelationships (e.g., over, below, adjacent, etc.) are set forth betweenelements in the following description and in the drawings. Theseconnections and/or positional relationships, unless specified otherwise,can be direct or indirect, and embodiments of the present invention arenot intended to be limiting in this respect. Accordingly, a coupling ofentities can refer to either a direct or an indirect coupling, and apositional relationship between entities can be a direct or indirectpositional relationship. As an example of an indirect positionalrelationship, references in the present description to forming layer “A”over layer “B” include situations in which one or more intermediatelayers (e.g., layer “C”) is between layer “A” and layer “B” as long asthe relevant characteristics and functionalities of layer “A” and layer“B” are not substantially changed by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements. It should benoted that the term “selective to,” such as, for example, “a firstelement selective to a second element,” means that the first element canbe etched and the second element can act as an etch stop.

The phrase “selective to,” such as, for example, “a first elementselective to a second element,” means that the first element can beetched and the second element can act as an etch stop.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

As previously noted herein, for the sake of brevity, conventionaltechniques related to semiconductor device and integrated circuit (IC)fabrication may or may not be described in detail herein. By way ofbackground, however, a more general description of the semiconductordevice fabrication processes that can be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention can be individually known, thedescribed combination of operations and/or resulting structures of thepresent invention are unique. Thus, the unique combination of theoperations described in connection with the fabrication of asemiconductor device according to the present invention utilize avariety of individually known physical and chemical processes performedon a semiconductor (e.g., silicon) substrate, some of which aredescribed in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into four general categories, namely, filmdeposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Semiconductordoping is the modification of electrical properties by doping, forexample, transistor sources and drains, generally by diffusion and/or byion implantation. These doping processes are followed by furnaceannealing or by rapid thermal annealing (RTA). Annealing serves toactivate the implanted dopants. Films of both conductors (e.g.,poly-silicon, aluminum, copper, etc.) and insulators (e.g., variousforms of silicon dioxide, silicon nitride, etc.) are used to connect andisolate transistors and their components. Selective doping of variousregions of the semiconductor substrate allows the conductivity of thesubstrate to be changed with the application of voltage. By creatingstructures of these various components, millions of transistors can bebuilt and wired together to form the complex circuitry of a modernmicroelectronic device. Semiconductor lithography is the formation ofthree-dimensional relief images or patterns on the semiconductorsubstrate for subsequent transfer of the pattern to the substrate. Insemiconductor lithography, the patterns are formed by a light sensitivepolymer called a photo-resist. To build the complex structures that makeup a transistor and the many wires that connect the millions oftransistors of a circuit, lithography and etch pattern transfer stepsare repeated multiple times. Each pattern being printed on the wafer isaligned to the previously formed patterns and slowly the conductors,insulators and selectively doped regions are built up to form the finaldevice.

The flowchart and block diagrams in the Figures illustrate possibleimplementations of fabrication and/or operation methods according tovarious embodiments of the present invention. Variousfunctions/operations of the method are represented in the flow diagramby blocks. In some alternative implementations, the functions noted inthe blocks can occur out of the order noted in the Figures. For example,two blocks shown in succession can, in fact, be executed substantiallyconcurrently, or the blocks can sometimes be executed in the reverseorder, depending upon the functionality involved.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments described. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

What is claimed is:
 1. A method for forming a semiconductor structure,the method comprising: forming a silicon fin on a silicon germaniumstrain relaxed buffer (SRB) layer; laterally forming a spacer on a sideof the silicon fin; performing a thermal anneal; and performing an etchto remove material formed by the thermal anneal; wherein the spacercomprises germanium oxide at least partially formed on at least part ofthe silicon fin.
 2. The method of claim 1, wherein: the thermal annealconverts at least part of the silicon germanium in the SRB layer tosilicon oxide.
 3. The method of claim 2, wherein: performing the etchcomprises performing on isotropic etch to remove the silicon oxide. 4.The method of claim 3, wherein: the isotropic etch comprises ahydrofluoric acid wet etch or dry etch.
 5. The method of claim 2,wherein: performing the etch comprises removing a water-solublegermanium oxide using a water solution.
 6. The method of claim 1,wherein: the thermal anneal is performed in an inert gas environment. 7.The method of claim 1, further comprising: filling areas of thesemiconductor with a shallow trench isolation area; and performing arecess to expose one or more fins of the semiconductor structure.
 8. Themethod of claim 1, wherein: the thermal anneal is performed at atemperature of approximately 450 to 700 degrees Celsius.
 9. The methodof claim 1, wherein: the thermal anneal is performed in a nitrogenatmosphere.
 10. The method of claim 1, further comprising: placing amask over one or more fin regions; and performing an etch of areas ofthe semiconductor structure exposed by the mask; wherein the etch isconfigured to remove exposed shallow trench isolation material andexposed fin material.